Kyoukaisenjou no Horizon

The story is set in a distant future where Japan is divided into feudal territories and conquered by other countries. There is a floating city named Musashi that is composed of eight ships in the skies. A war that will determine the fate of the world will be fought by students on the Musashi.

In the far future, humans abandon the devastated Earth and ascend to the upper world "Tenjo", taking on new, god-like form. But even with their newfound "Godhood", humanity eventually fell into war, resulting in the collapse of Tenjo and the very law of causation, and humanity, having lost their divine powers, returns to the Earth, grown largely uninhabitable, with the exception of a portion of the Far-East (modern-day Japan...